General requirements for cutting metals, especially metals such as steel, certain ceramics, and concrete, under water, have led to the development of a series of exothermic burning rods primarily based upon various thermite reactions involving the combustion of oxides of iron in the presence of oxygen atmospheres. In general, these rods are known to comprise an essentially ferrous burning element, which may be augmented with aluminum or a chemically related metal of the group comprising aluminum, magnesium, titanium, which is combusted in the presence of an oxygen atmosphere to produce an intensely hot oxidizing flame. Excess oxygen provides a burning or oxidizing capability which aids in the process of burning through a material to be cut.
Such rods and torches utilizing such rods have come into widespread use in underwater cutting. Oxygen is provided through the rod under a pressure sufficient to displace the water in the vicinity of the cutting element; the rod, being of a metallic composition, is ignited by creating an electrical circuit involving the rod and the object to be cut, supplying a relatively high amperage current so that contacting the rod to the element to be cut creates a large spark with sufficient electrical heat to ignite the rod.
The most recent developments in this type of thermite or exothermic burning rod may be seen in U.S. Pat. No. 4,069,1107 to Brower, which describes an elongated metallic rod suitable for the conduction of electricity having an insulating outer coating and having a plurality of interior elements running its length. With one exception, the elements are primarily of an iron composition. The exception is that at least one element, constructed of metal from the metallic group comprising aluminum, magnesium, titanium, or their alloys is included so as to provide the aluminum, iron, and oxygen mixture required for the classic thermite reaction. The rods are gripped in a pressure tight collect chuck in a specially designed torch handle which provides a continuous flow of oxygen at a pressure generally around 140 pounds per square inch over the ambient pressure in which the rod is expected to work. The oxygen passes the length of the rod through passages which are created by the spaces between the interior rods within the outer rod-holding element. An electrical source is provided to the rod capable of providing several hundred amperes of current, usually in the vicinity of 150-400 amperes. The entire rod and handle are part of a circuit which is completed through the object to be cut. Contacting the rod tip in the handle to the object to be torched creates an intense spark of heat which ignites the rod. It is known that once the rod is ignited, so long as oxygen continues to be applied to the burning iron element, the thermite reaction will continue the burn without further addition of electrical energy.
Rods of this nature, however, have serious problems. First, the fact that the thermite mixture is comprised of a finite number of elements which are either iron or aluminum creates a definite limitation on the achievable ratios of aluminum to iron, and it is found that the Brower rod normally runs 16 to 20 percent aluminum as a minimum in order to meet the requirement of having an integral number of rods, while having sufficient interior free area for the flow of oxygen. It is found that such colocated individual elements will independently burn once ignited in the oxygen atmosphere that surrounds them. The overall reaction is both uneven and colder than a theoretical thermite reaction should be, and thus the rod will not cut all objects which could be cut by a pure thermite reaction.
In addition, since the rod is ignited by electrical arcing, interior electrical arcing within the rod will create points of burning inside the rod. This process creates a situation in which an interior burn within the rod will cause the rod to burn, jetting a hole through a side of the rod, bleeding off the oxygen pressure, and rendering the rod unusable or dangerous.